[PATCH 3/3] Allow removal of current Slab

[Owen Smith <owen.smith@xxxxxxxxx>]

From: Owen Smith <owen.smith@xxxxxxxxxx>

When all Objects in the current Slab have been freed, its possible
that the current Slab will be destroyed. Its not guaranteed that the
current Slab is the only Slab in the SlabList, as objects can be returned
in a different order than allocated, especially after objects have been
reused.

Walk the Cursor back to the previous Slab (or SlabList header) and allow
for the possibility that the current Slab may be full during the CacheGet
call (which will require creation of another Slab)

Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>
---
 src/xenbus/cache.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/src/xenbus/cache.c b/src/xenbus/cache.c
index 07dcd56..e2aa137 100644
--- a/src/xenbus/cache.c
+++ b/src/xenbus/cache.c
@@ -471,14 +471,11 @@ CacheDestroySlab(
     ASSERT3U(Cache->Count, >=, CacheMaskSize(Slab->Allocated));
     Cache->Count -= CacheMaskSize(Slab->Allocated);
 
-    //
-    // The only reason the cursor should be pointing at this slab is
-    // if it is the only one in the list.
-    //
     if (Cache->Cursor == &Slab->ListEntry)
-        Cache->Cursor = &Cache->SlabList;
+        Cache->Cursor = Slab->ListEntry.Blink;
 
-    RemoveEntryList(&Slab->ListEntry);
+    if (RemoveEntryList(&Slab->ListEntry))
+        Cache->Cursor = &Cache->SlabList;
 
     ASSERT(Cache->Cursor != &Cache->SlabList ||
            IsListEmpty(&Cache->SlabList));
@@ -614,17 +611,17 @@ again:
         Slab = CONTAINING_RECORD(ListEntry, XENBUS_CACHE_SLAB, ListEntry);
 
         Object = CacheGetObjectFromSlab(Slab);
-        ASSERT(Object != NULL);
 
-        if (CacheMaskCount(Slab->Allocated) == CacheMaskSize(Slab->Allocated))
+        if (CacheMaskCount(Slab->Allocated) == CacheMaskSize(Slab->Allocated)) 
{
             Cache->Cursor = Slab->ListEntry.Flink;
+            if (Object == NULL)
+                goto again;
+        }
     }
 
     if (Object == NULL) {
         NTSTATUS status;
 
-        ASSERT3P(Cache->Cursor, ==, &Cache->SlabList);
-
         status = CacheCreateSlab(Cache);
         if (NT_SUCCESS(status)) {
             ASSERT(Cache->Cursor != &Cache->SlabList);
-- 
2.39.0.windows.1